This invention relates to a recording material having a color former coating layer formed by coating on a surface of a base sheet a coating composition including microcapsules each encapsulating a hydrophobic material containing an electron donating organic chromogenic material and more particularly to such recording material having a good ballpoint pen writability and a good printability.
Among recording materials there are well known pressure-sensitive copying papers and heat-sensitive recording papers which utilize the color developing reaction between electron donating organic chromogenic material (hereinafter referred to as "color former") and electron accepting acidic reactant material (hereinafter referred to as "acceptor"). In pressure-sensitive copying paper at least one of the color former and the acceptor is contained in microcapsules so as to be isolated from the other and they become into contact with each other by rupturing such microcapsules to develop a color. In a most typical type of pressure-sensitive copying paper minute oil droplets in which the color former is dispersed or dissolved are encapsulated and coated onto papers.
Usually the pressure sensitive copying system utilizing the above-mentioned pressure sensitive copying papers consists of three kinds of sheets such as a top sheet, at least one middle sheet and a bottom sheet, wherein the top sheet is coated on the underside thereof with a composition consisting mainly of pressure rupturable microcapsules each enclosing an oil droplet containing a color former dissolved or dispersed therein, the middle sheet is coated on the upperside thereof with another composition consisting mainly of an acceptor and also is coated on the underside thereof with the composition of microcapsules containing an oil droplet in which a color former is dissolved or dispersed and the bottom sheet is coated on the upperside thereof with the composition of an acceptor. Any partial pressing on the upperside of the top sheet of the thus prepared copying system with a pen or a typewriter will break the microcapsules positioned on the pressing, resulting in making the color former react with the acceptor so as to develop a color only on the part pressed.
In another pressure sensitive copying system, there are disposed on one surface of the same sheet both the acceptor and the microcapsules containing oil droplets in which the color former is dissolved or dispersed. This system is known as the "self contained" system.
Among known color former compounds for pressure sensitive copying paper there are included triarylmethane derivatives such as 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide (CVL), 3,3-bis(p-dimethylaminophenyl)phthalide, 3-(p-dimethylaminophenyl)-3-(1,2-dimethylindole-3-yl)phthalide, 3-(p-dimethylaminophenyl)-3-(2-methylindole-3-yl)phthalide, 3,3-bis(1,2-dimethylindole-3-yl)-5-dimethylaminophthalide, 3,3-bis-(1,2-dimethylindole-3-yl)-6-dimethylaminophthalide, 3,3-bis-(9-ethylcarbazole-3-yl)-5-dimethylaminophthalide, 3,3-bis-(2-phenylindole-3-yl)-5-dimethylaminophthalide, 3-p-dimethylaminophenyl-3-(1-methylpyrrole-2-yl)-6-dimethylaminophthalide, diphenylmethane derivatives such as 4,4'-bis-dimethylaminobenzhydrylbenzylether, N-halophenyl-leucoauramine, N-2,4,5-trichlorophenyl-leucoauramine, Xanthene derivatives such as rhodamine-B-anilinolactam, rhodamine-(p-nitro-anilino)lactam, rhodamine-(p-chloroanilino)lactam, fluoran compounds such as 3-dimethylamino-7-methoxyfluoran, 3-diethylamino-7-methoxyfluoran, 3-diethylamino-6-methoxyfluoran, 3-diethylamino-6-chlorofluoran, 3-diethylamino-6-chloro-7-methylfluoran, 3-diethylamino-6,7-dimethylfluoran, 3-diethylamino-7-acethylaminofluoran, 3-diethylamino-6-methylaminofluoran, 3,7-diethylaminofluoran, 3-diethylamino-7-dibenzylaminofluoran, 3-diethylamino-7-(methylbenzylamino)fluoran, 3-diethylamino-7-(N-chloroethyl-N-methylamino)fluoran, 3-diethylamino-7-diethylaminofluoran, 3-(N-ethyl-N-p-toluyl)amino-6-methyl-7-phenylaminofluoran, thiazine derivatives such as benzoylleucomethyleneblue, spiropyrane derivatives such as p-ethyl-spiro-dinaphthopyrane, 3,3'-dichlorospiro-dinaphthopyrane, 3-benzylspiro-dinaphthopyrane, 3-methylnaptho-( 3-methoxy-benzo)-spiropyrane and 3-propyl-spiro-dibenzopyrane. These compounds are used either solely or in combination.
Various natural and synthetic oils are used either solely or in combination for dissolving or dispersing the color former compound. Among them there are included cotton seed oil, linseed oil, soybean oil, castor oil, alkylbenzene, hydrogenated terphenyl, hydrogenated terphenyl derivatives, alkylbiphenyl, alkylnaphthalene, diarylalkane, kerosene, paraffin and naphthene oil.
The most typical method for making oil droplet-containing microcapsules for the above mentioned purpose is to utilize the coacervation technique, e.g., as disclosed in U.S. Pat. No. 2,800,457 and U.S. Pat. No. 2,800,458. Various other methods for making oil droplet-containing microcapsules are also useful. Among them there are included the interfacial polymerization technique as disclosed Japanese Patent Publication No. 771 of 1967 and the in-situ polymerization technique as disclosed in Japanese Laid Open Patent Publication No. 9, 079 of 1976.
Among the useful acceptor compounds to develop a color in contact with an organic color former, there are included inorganic acid materials such as acidic clay, activated clay, calcined activated clay and attapulgite, and organic acceptors such as phenolic compounds, phenole-aldehyde polymers, phenol-acetylene polymers, maleic acid-rosin resin, hydrolyzed styrene-maleic anhydride copolymer, aromatic carboxylic acids e.g. salicylic acid and their derivatives and their metal salts.
Pressure sensitive copying papers found their usefulness in various commercial applications such as computer output recording papers, business forms and copying slips. In some cases the microcapsule coated surface of the pressure sensitive copying paper has a form printing for writing thereon by a pencil or ballpoint pen. In those cases the microcapsule coated surface of the pressure sensitive copying paper must have a good printability and a good ballpoint pen writability. However, there are many difficulties to be overcome to achieve this requirement. For example, in case of the ballpoint pen writing, the oil included in microcapsules often causes coagulation of the ballpoint pen ink and produces ink and oil smudges adhered to a ballpoint pen ball with the result that smooth rotation of the ballpoint pen ball is prevented.
Some attempts have been made to overcome the above mentioned difficulties. For example, it was proposed to add inorganic pigment particles to the microcapsule coating composition. Another attempt was to form an overcoating layer of inorganic pigment particles on the microcapsule coating layer, as disclosed in Japanese Laid Open Patent Publication No. 51,215 of 1977. However, these two attempts involve to decrease the color formability which is one of the most important requirements for the pressure sensitive copying papers. A further attempt was to add a carbazole derivative to the oil encapsulated in the microcapsules, as disclosed in Japanese Laid Open Patent Publication No. 150,118 of 1977. The attempt fails to obtain a satisfactorily good ballpoint pen writability as desired.
The principal object of the invention is to provide an improved recording material having a color former microcapsule coating layer in which the microcapsule coated surface has a good ballpoint pen writability and a good printability without sacrificing the color formability of the color former layer.
Other objects and advantages of the invention will be apparent from the following description.